Electric arc welding processes have become one of the most important welding techniques, particularly for joining steels. Electric arc welding generally involves the supplying of either direct or alternating current for creating an electric arc which generates enough heat to melt metal for the weld. Although arc welding produces welds having high join quality and join strength, arc welding has some drawbacks. For example, arc welding has traditionally resulted in distortion and spatter. Prior to the present invention, there was no cost effective or efficient way to control the electric discharges produced in arc welding technology.
It is known to control electric discharge by using high power laser sources which thermally ionize the local atmosphere. This process requires the use of ultraviolet lasers, which are strongly absorbed in the atmosphere, or very high power lasers which cause thermal breakdown in the local atmosphere. This approach tends to generate localized regions of ionization where the electric discharge is initiated. Guiding the electric discharge over a long path is difficult since both the ionization and the breakdown processes cause strong attenuation and scattering of the laser beam. Additionally, since breakdown requires a high field strength, the breakdown process tends to be localized at the laser focus rather than uniformly distributed along the path length of the laser beam itself.
The present invention discloses a new approach of controlling electric discharges by the production of excited molecules along the desired path of the discharge. More particularly, the invention discloses an approach to controlling electric discharges by the production of metastable molecules using a low power laser. The present invention is advantageous in that:
1.) a low power laser may be used to vibrationally excite predetermined molecules so as to guide an electric discharge; PA1 2.) vibrational states of the molecules may be excited with little, if any, rotational or translational molecular energy conversion, i.e., the molecules do not experience generalized heating; PA1 3.) the present invention may provide arc initiation, path stablilization and discharge constriction; PA1 4.) the laser beam may be pulsed; PA1 5.) the arc may be pulsed; PA1 6.) both laser beam and arc may be pulsed; PA1 7.) low powered, relatively inexpensive, lasers may be used to control electric discharges; PA1 8.) rapid arc movement and accurate arc position are achieved; PA1 9.) the discharge can be constricted to a very small cross section allowing constriction of an arc into a high power density heat source; and PA1 10.) small area, high power density discharges may be controlled allowing for small welds (e.g., smaller than 3 mm wide) and deep penetration welding (e.g., where depth of penetration is greater than weld width).